Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Polyvinyl chloride (PVC) without modification is very brittle, and thus it is typically made more flexible by plasticization with low or high molecular weight plasticizers. A wide variety of materials have been used as plasticizers, generally liquids of viscosities such that they are usually characterized as oils or syrups. The first plasticizers to be used for this purpose were either low molecular weight liquid monomeric organic phthalates or phosphate esters or low molecular weight oligomeric polyesters, which are in effect syrupy liquids. Even materials designated as “polymeric” that have molecular weights of a few thousand or below are very viscous liquids at 25° C.
An important component of polyvinyl chloride plastisols is a liquid plasticizer of low molecular weight that causes the PVC resin to flow and the end product to be flexible. Plastisols are suspensions of small PVC particles in liquid plasticizer. They are made by mixing the PVC particles and the plasticizers in a mixer until well-blended. Plastisols flow as a liquid or paste and can be poured or spread into a heated mold. Above the Tg for the composition, the small PVC particles begin to absorb the plasticizer molecules. Further heating to about 160 to 170° C. or higher causes the mixture to fuse, forming an entangled molecular network. On cooling the mold below 60° C., a flexible, permanently plasticized solid product results. Aside from molding, plastisols are commonly used to prepare geomembrane or architectural canvas, as a textile ink for screen printing and as a coating, for example a dip-coating, particularly in outdoor structures (roofs, furniture), among other applications.
Disadvantageously, conventional liquid plasticizers have low molecular weights such that after a certain period of time they may migrate to the surface of the PVC or a product made from the PVC. Eventually, the liquid plasticizers can evaporate, or be washed away, leaving a stiff, brittle, or fragile PVC product.
Therefore, there is a need to produce a modified plasticizer that will not evaporate or migrate out of a plastisol or a product made from the plastisol. Alternatively, the modified plasticizer can reduce or substantially reduce the evaporation or migration of the plasticizer.
Some high molecular weight materials have been used to plasticize PVC. For example, U.S. Pat. No. 3,780,140 describes plasticizers consisting of copolymers of ethylene, carbon monoxide and a third monomer that can be a vinyl ester or an acrylate or methacrylate for use in plastics such as polyvinyl chloride (PVC), nitrocellulose, etc.
At about the same time, it was also recognized that ethylene vinyl acetate copolymers with high vinyl acetate contents were effective polymeric plasticizers for polyvinyl chloride. Both ethylene vinyl acetate copolymers and the copolymers described in U.S. Pat. No. 3,780,140 are used today to plasticize nonporous polyvinyl chloride.
The ethylene copolymers are routinely used in flexible PVC formulations for use in melt-processable rubbers, flexible PVC sheeting, pond liners, membranes, wire coatings, cable jackets, injection molded parts, and other profile-extruded articles.
Polyvinyl chloride containing both conventional low molecular weight plasticizers and high molecular weight plasticizers is described in U.S. Pat. No. 3,780,140. Incorporating the high and low molecular weight plasticizers with the polyvinyl chloride is accomplished by blending a solution of polyvinyl chloride in tetrahydrofuran with a solution of the high and low molecular weight plasticizers in tetrahydrofuran, followed by evaporating the tetrahydrofuran.
U.S. Pat. No. 6,147,170 describes novel plasticizer compositions that comprise ethylene copolymers combined with reactive ultraviolet (UV) absorbing agents. Copolymers of ethylene/carbon monoxide/termonomer were grafted with dicarboxylic acid anhydride groups such as maleic anhydride, reacted with polymerizable UV stabilizers, and used as plasticizers for polymers such as PVC.
U.S. Pat. No. 7,737,210 describes a composition comprising or produced from polyvinyl chloride, filler, and an impact strength-retaining amount of a modifier wherein the modifier may be an ethylene copolymer including copolymers of ethylene/carbon monoxide/termonomer, an acid anhydride- or acid monoester-modified polyolefin, or combinations thereof.
European Patent No. EP0587727 describes a process for preparing a free-flowing plasticized powdered PVC composition. The process comprises blending a combination of a solid high molecular weight ethylene copolymer plasticizer and a low molecular weight liquid plasticizer with porous polyvinyl chloride powder having substantially no impermeable skin at temperatures from 70 to 130 ° C. until a free flowing powdered plasticized polyvinyl chloride is obtained.
Nevertheless, there remains a need for PVC compositions that are easily processed, that have improved stability with respect to aging and UV attack, or that have improved mechanical properties such as resistance to punctures and tears.